I liked this book even better than the first. Sam and Robert are still having lots of smokin' hot sex but they are also maturing and having to deal with life's and ups and downs. I found those scenes an emotional reflection of how strong their relationship had become on how they handled and dealt with them, communicated and showed their love.
We also get some supporting characters, we get Robert rocking Sam's world in his uniform, Sam still being a horndog and Tom (Sam's dad) working with Sam to make Robert blush at any opportunity :) while still being a really cool dad.
If you liked the first On Fire, you'll like this one.